diff -up ksh-20120801/src/cmd/ksh93/include/jobs.h.locking ksh-20120801/src/cmd/ksh93/include/jobs.h

--- ksh-20120801/src/cmd/ksh93/include/jobs.h.locking	2014-06-27 15:51:07.144923719 +0200

+++ ksh-20120801/src/cmd/ksh93/include/jobs.h	2014-06-27 15:52:56.463272276 +0200

@@ -149,15 +149,18 @@ extern struct jobs job;

 #define vmbusy()	0

 #endif

-#define job_lock()	(job.in_critical++)

+#define asoincint(p)  __sync_fetch_and_add(p,1)

+#define asodecint(p)  __sync_fetch_and_sub(p,1)

+

+#define job_lock()	asoincint(&job.in_critical)

 #define job_unlock()	\

 	do { \

 		int	sig; \

-		if (!--job.in_critical && (sig = job.savesig)) \

+		if (asodecint(&job.in_critical)==1 && (sig = job.savesig)) \

 		{ \

-			if (!job.in_critical++ && !vmbusy()) \

+			if (!asoincint(&job.in_critical) && !vmbusy()) \

 				job_reap(sig); \

-			job.in_critical--; \

+			asodecint(&job.in_critical); \

 		} \

 	} while(0)